1. Field of the Invention
The present invention relates to a field of liquid crystal display technology, and more specifically to a pixel electrode structure and a liquid crystal display (LCD) panel.
2. Description of the Prior Art
An LCD is one of the most popular flat panel displays. The LCD includes: a pair of substrates having a field emission electrode (such as a pixel electrode and a common electrode) thereon; and a liquid crystal layer sandwiched between the substrates. An electric field is generated in the liquid crystal layer when a voltage is applied to the field emission electrode. The electric field decides the alignment of liquid crystal molecules in the liquid crystal layer, thus an image is displayed on the LCD when the polarization of incident lights penetrating the liquid crystal layer is adjusted.
At present, a technology called polymer stabilized vertical alignment (PSVA) has been developed in the industry. In the technology, a suitable concentration of monomer is mixed in a liquid crystal material, and then is uniformly shaken. Then, the mixed liquid crystal material is placed on a heater, and then is heated to an isotropic state. The liquid crystal mixture is returned to a nematic state when the liquid crystal mixture is cooled to room temperature. Then, the liquid crystal mixture is injected into a liquid crystal cell, and then a voltage is applied. When the liquid crystal molecules are stably arranged by applying a voltage, the monomer is polymerized by way of an ultraviolet light or heating to form a polymer layer, so as to achieve the object of a stable alignment.
FIG. 1 is a schematic view of a structure of a pixel electrode often used in a universal VA mode LCD.
The pixel electrode of the universal VA mode LCD of FIG. 1 is designed as a “” shape. The pixel electrode includes a strip shaped vertical main trunk, a strip shaped horizontal main trunk, and a plurality of strip shaped branches. There is a certain angle between the strip shaped branches and the horizontal main trunk, respectively. Generally, an angle between the strip shaped branches and the horizontal main trunk is ±45 degrees or ±13 degrees. Each of the strip shaped branches, the vertical main trunk, and the horizontal main trunk are located on the same plane. The center of the vertical main trunk and the center of the horizontal main trunk are vertically crossed. The vertical cross of the center means that the vertical main trunk is perpendicular to the horizontal main trunk. The area around the center of the vertical cross is the central area of the single pixel electrode. The whole pixel area is equally divided into four domains by the vertical main trunk and the horizontal main trunk. The strip shaped branches, which are at a certain angle to the vertical main trunk or the horizontal main trunk, are tiled in each of the four domains. Thus, the “” shaped electrode of FIG. 1 is formed. In the “” shaped electrode, the upper and lower parts thereof and the left and right parts thereof are mirror symmetrical, respectively.
FIG. 2 shows a schematic view of the tilt of liquid crystals after a voltage (about 0-4 V; arrows are used to represent an applied voltage) is applied to the pixel electrode of FIG. 1.
As shown in FIG. 2, the liquid crystals are gradually tilted from the outside of the pixel electrode to the inside of the pixel electrode when a “” shaped electrode structure which is widely used is energized. The angle of the tilt is along the direction of the branches. In the four domains, the liquid crystals of the upper-right domain thereof have a tilting direction of 45 degrees; the liquid crystals of the upper-left domain thereof have a tilting direction of 135 degrees; the liquid crystals of the lower-left domain thereof have a tilting direction of 225 degrees; the liquid crystals of the lower-right domain thereof have a tilting direction of 315 degrees. The liquid crystals of the upper-left domain and the upper-right domain are gradually tilted from the outside of the pixel electrode to the inside of the pixel electrode when a voltage is applied, since the symmetric strip shaped branches of the upper-left domain and the upper-right domain are diverged outward along the center of the vertical main trunk. The angle of the tilt is along the direction of the branches. At this point, the tilt of the liquid crystals between two intersecting lines of the symmetric strip shaped branches crossing the vertical main trunk is very easy to be in a chaotic state. Similarly, the tilt of the liquid crystals between two intersecting lines of the symmetric strip shaped branches of the upper-left domain and the lower-left domain crossing the horizontal main trunk is also very easy to be in a chaotic state, thus dark fringes are easily produced on the “+” shaped trunk of a “” shaped pixel electrode, so that the display effects of the “+” shaped trunk are poor.